Planting leafy green vegetables is easy, but it's all in the timing. Knowing when to plant greens (such as spinach, kale, and lettuce) depends on your climate and if the leaf vegetables are heat- or cold-tolerant.
Greens grow year-round in areas with mild summers and winters, such as the West Coast. For most other areas, spring and fall are the best times to grow greens. Greens can be sown directly in the garden starting in spring and, in cool areas, planted throughout the summer until September. If you want to get a jump on the season, start seeds four to six weeks before the last frost date in your area so they can be planted two to three weeks later.
Gardeners in mild winter areas such as Arizona, Texas, and Florida may prefer a winter crop of greens because the weather is more favorable. Summer is too hot to germinate the seeds and grow the traditional types of lettuce and greens. For a winter crop, sow seeds indoors in fall to be transplanted into the garden a month later.
If you don't have the right climate for year-round growing but love fresh greens, here are some guidelines for growing your own salad 12 months of the year in spite of cold winters and hot summers:
Choose the right varieties: To grow a winter greens crop in cold-winter areas (hardiness zone 5 or 6) without season extenders, plant spinach, arugula, claytonia, mizuna, and winter lettuce varieties such as 'Winter Density'. To grow greens through summer in warm areas (hardiness zone 7 and warmer) choose greens that like the heat, such as Malabar or New Zealand spinach.
Time your planting: Start heat-loving greens in late spring so they mature during summer's heat. For winter greens in the cold areas, start cold-tolerant plants in fall so they mature to full size before the bitter cold weather of December. The greens don't have to grow during the short winter days and cold temperatures — they just need to stay alive.
Keep the soil fertile: Successive crops of greens take nutrients out of the soil, so after every crop you remove, add a 2- to 3-inch layer of compost to the soil and work it in well.
Protect the plants: During the summer heat, use shade cloth to block the afternoon sun. In the North, protect greens through the cold winter by growing them in cold frames.
Here are a couple of other tips for planting greens at the right time:
Stagger your plantings to avoid producing too large a supply: Planting small, 2-to-4-foot patches of greens every 2 weeks throughout the growing season, which is referred to as succession planting, is the best way to ensure a manageable supply of lettuce all summer long. In warm areas, you may want to skip planting in midsummer because lettuce will bolt from the heat.
Give iceberg (crisphead) lettuce the environment it needs to thrive: Iceberg lettuce likes cool temperatures (50 to 60 degrees F) throughout the growing season, especially when it's trying to form a head.
For northern and southern gardeners, fall planting is the key. In warm areas, start seeds indoors in September; then place the seedlings in the garden in October or November. In cooler climates, start seeds indoors in July to plant in the garden in August or September. Keep plants well watered and feed them every three weeks with fish emulsion. By the cool days of fall, your iceberg lettuce heads should form.